Synthesis and Crystal Structures of Two Metal Urea Nitrates

Abstract

Cu(urea)2(H2O)3(NO3).(urea)(NO3) (1) and Zn(urea)4(H2O)2·2(NO3) (2) have been obtained from the corresponding metal nitrates and urea in warm aqueous solvent. These are unusual examples of complexes of transition metals coordinated only by urea and water. 1 crystallizes in the monoclinic space group P21/m with unit cell parameters a = 9.489(3), b = 13.059(3), c = 7.103(2) A and β = 100.28(3)°. The copper ion occupies a 2e position on a mirror plane and displays four short Cu–O bonds (2 × Cu–OH2 and 2 × Cu–O=C(NH2)2) and two much longer contacts (Cu–OH2 and Cu–ONO2) consistent with a Jahn–Teller distortion. Between the cations are located unbound urea and nitrate. 2 crystallizes in the monoclinic space group P21/n with a = 6.4239(11), b = 17.690(4), c = 7.5877(13) A and β = 91.138(14)°. The zinc ion resides on the 2a position, an inversion centre, and displays pseudo–octahedral coordination geometry. It is coordinated by four equatorial urea and two axial water molecules. The four molecules of urea are nearly planar and form N–H···O intramolecular hydrogen bonds. Unbound charge-balancing nitrate is also present. In each compound there is extensive intermolecular hydrogen bonding between the water, urea, and nitrate present. Pyrolysis of the compounds under 10% hydrogen in nitrogen at 300 °C was found to yield metallic copper in the case of 1 and zinc oxide for 2. The structures of two new metal urea nitrates have been determined at low temperature